Installations for filling receptacles by weight are known that comprise filler spouts connected to the bottom of a common feed vessel. When the feed vessel is subjected to atmospheric pressure, the pressure at the bottom of the vessel is given by the depth of liquid in the vessel. In order to obtain a satisfactory flow rate of liquid through a large number of filler spouts while having a feed vessel that presents reasonable dimensions, it is therefore necessary to put the vessel under pressure by injecting compressed air above the liquid.
In order to enable accurate measuring to be performed by a weighing device, it is also desirable for the pressure to be as constant as possible at the inlet to the filler spout. For this purpose, the feed vessel is generally maintained with liquid at a constant level and with the pressure of the compressed air above the liquid being regulated as a function of a setpoint pressure.
In existing devices, this regulation of the pressure of the air above the liquid is performed by means of a servo-valve having an inlet orifice connected to a source of air under pressure, an outlet orifice connected to the feed vessel, and an exhaust orifice connected to the atmosphere. The servo-valve also has a control connection member serving either to close the outlet orifice, or to put the inlet orifice into communication with the outlet orifice, or else to put the outlet orifice into communication with the exhaust orifice. Air pressure in the feed vessel is thus regulated jerkily which runs the risk of leading to a pumping phenomenon.